702 PROPERTIES, HARVESTING AND DISPOSAL OF RESIN. 



cambium into two parts, one in the wood and the other in 

 the bast, so that turpentine cannot pass from one to the other ; 

 only with the new year's growth is the connection between 

 them restored. 



All wound-parenchyma (occlusion-tissue) in wood is an 

 abnormal holder of turpentine (p. 1'29) ; such a tissue con- 

 tains certain wounds that are externally invisible, as are some 

 frost wounds, while others are externally visible and cause an 

 exudation of resin between the new and dead tissues, so that the 

 swelling is more or less encrusted with resin. Abnormal resin- 

 ducts occur also in genera which have also normal ducts (spruce, 

 larch, pines and Douglas-firs), as well as in the other conifers. 

 They are of pathological origin, as Tschich showed in Berne 

 that pathological conditions, especially those due to root-fungi, 

 also cause excessive formation of resin-blisters in the bark of 

 silver-fir and Douglas-fir, as was proved by Mayr, in 1893. 



The course of resin-ducts in the bark and needles varies in 

 different species ; in spruces and Douglas-firs, both the ducts 

 of the needles pass into the cortex and there unite with the 

 vertical ducts that are 8, 13, 21, 26, etc. in number. The 

 cortical ducts of two years shoots form two exclusive systems 

 without any connection (Fig. 369 a. c.). 



If a vertical cortical duct is cut, only a small quantity of 

 resin exudes. When rhitidome is formed, on the south side 

 of a tree, in the seventh year, on the north side in the tenth 

 year and in a dense wood in the fifteenth year of the tree, the 

 first cortical resin-ducts are cut off, so that spruce and 

 Douglas-firs exhibit longitudinal ducts only up to the thirtieth 

 year ; the bast under the rhitidome is, however, rich in hori- 

 zontal ducts. In silver-firs and hemlock-spruces, the course 

 of the vertical ducts in the cortex is the same as in the spruce ; 

 but parts of the cortex of both these genera, as well as 

 Douglas-fir, swell into blisters which may be tapped for resin 

 commercially. The ducts remain active for a number of 

 years, in silver-fir for eighty years ; the bast contains no 

 resin-ducts. In pines, only one and two years old plants, 

 that bear simple needles, are constructed after the pattern of 

 the above genera, the clusters of needles (2, 3 and 5), which 

 appear later, bear two resin-ducts in the two edges of each 



